1. Field of the Invention
The present invention generally relates to a gas diffuser for semiconductor device fabrication and a reaction furnace provided with the gas diffuser. More particularly, the present invention relates to a gas diffuser for semiconductor device fabrication in which the thickness of the gas diffuser and the density of nozzles penetrating the gas diffuser are designed to deposit uniform layers on a target object, and to a reaction furnace using the gas diffuser.
2. Description of the Related Art
In general, as shown in FIG. 1, a reaction furnace for fabricating semiconductor devices, such as CVD equipment or a dry etcher, has a gas diffuser 12 disposed in the upper portion of a space which has an exhaust hole 10 formed to discharge a gas downwards, and a support plate 14 for supporting a wafer 1 held in the lower portion of the space.
Such a conventional gas diffuser 12 has the form of a hermetic cylinder with a hollow formed inside. The gas diffuser 12 is provided with a gas inlet 16 opened upward for gas to enter the hollow, and a disk-shaped diffusion plate 18 disposed below the hollow and having a plurality of nozzles 20 to guide and control the stream of gas pouring out of the hollow. The nozzles 20 are arranged in a uniform density throughout diffusion plate 18.
With that construction, gas or liquid descends from the gas diffuser 12 to the inside of the reaction furnace so that an even film is deposited on the surface of a target object or a uniform etching is carried out in the course of a process for fabricating semiconductor devices.
Actually, it is very difficult to obtain films with a desired uniformity and many efforts have been made to optimize the form of the gas diffuser and the reaction furnace, including rotation of the wafer support plate 14. Such rotation may cause an increase in the uniformity of deposited films in the circumferential direction of the wafer, but has a limitation in increasing the uniformity of films in the radial direction of the wafer, and uniformity in the radial direction is considered more important as the wafer diameter increases.